\documentclass[12pt]{article}

\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage{amsthm}
\usepackage{amsmath,amssymb}
\usepackage{parskip}
\usepackage{graphicx}
\usepackage[normalem]{ulem}
\usepackage{titling}
\usepackage[shortlabels]{enumitem}
\usepackage{multirow}
\usepackage{dsfont}
\usepackage{pdfpages}
\usepackage{tikz} 

% theorem styles
% with number
\newtheorem{corollary}{\bf Corollary}[section]
\newtheorem{definition}{\bf Definition}[section]
\newtheorem{proposition}{\bf Proposition}[section]
\newtheorem{Axiom}{\bf Axiom}
\newtheorem{theorem}{\bf Theorem}[section]
\newtheorem{lemma}{\bf Lemma}[section]
\newtheorem{example}{\bf Example}[section]
\newtheorem{remark}{\bf Remark}[section]
\newtheorem{Algorithm}{\bf Algorithm}[section]
\newtheorem{property}{\bf Property}[section]
\newtheorem{note}{\bf Note}
% with out number
\newtheorem*{corollary*}{\bf Corollary}
\newtheorem*{definition*}{\bf Definition}
\newtheorem*{proposition*}{\bf Proposition}
\newtheorem*{Axiom*}{\bf Axiom}
\newtheorem*{theorem*}{\bf Theorem}
\newtheorem*{lemma*}{\bf Lemma}
\newtheorem*{example*}{\bf Example}
\newtheorem*{remark*}{\bf Remark}
\newtheorem*{Algorithm*}{\bf Algorithm}
\newtheorem*{note*}{\bf Note}
\newcommand{\reff}[1]{Figure~\ref{#1}}
\newcommand{\reftb}[1]{Table~\ref{#1}}

\newcommand\round[1]{\left[#1\right]}

% mathbb and mathcal often used letters
\newcommand{\Z}{\mathbb{Z}}
\newcommand{\N}{\mathbb{N}}
\newcommand{\Q}{\mathbb{Q}}
\newcommand{\R}{\mathbb{R}}
\newcommand{\C}{\mathcal{C}}
\newcommand{\I}{\mathbb{I}}
\newcommand{\1}{\mathds{1}}
\newcommand{\F}{\mathbb{F}}
\newcommand{\Fp}{\F_{p}}

% text command
\newcommand{\suchthat}{\text{ s.t. }}
\newcommand{\andtext}{\text{ and }}
\newcommand{\ortext}{\text{ or }}
\newcommand{\none}{\text{ NONE }}
\newcommand{\bc}{\quad \text{ because }}
\newcommand{\modulo}[1]{\text{ (mod }#1)}
\newcommand{\im}{\text{im}}
\newcommand{\cirpu}[1]{\text{(#1)}}
\newcommand{\rota}[1][\theta]{\rho_{#1}}
\newcommand{\tran}[1][v]{t_{#1}}
\newcommand{\iso}{\approx}
\newenvironment{solution}{\par\textit{Sol.}}{\par}
\newcommand{\series}[1][n]{\sum_{#1=1}^{\infty}}
\newcommand{\limil}{\lim\limits}
\newcommand{\inflim}[1][n]{\limil_{#1\rightarrow\infty}}


\usepackage{mathtools}

\DeclarePairedDelimiter\abs{\lvert}{\rvert}%
\DeclarePairedDelimiter\norm{\lVert}{\rVert}%

% Swap the definition of \abs* and \norm*, so that \abs
% and \norm resizes the size of the brackets, and the 
% starred version does not.
\makeatletter
\let\oldabs\abs
\def\abs{\@ifstar{\oldabs}{\oldabs*}}
%
\let\oldnorm\norm
\def\norm{\@ifstar{\oldnorm}{\oldnorm*}}
\makeatother

% double indent
\newcommand{\iindent}{\indent\indent}

% Margins
\usepackage[top=2.5cm, left=3cm, right=3cm, bottom=4.0cm]{geometry}
% Colour table cells
% \usepackage[table]{xcolor}

% Get larger line spacing in table
\newcommand{\tablespace}{\\[1.25mm]}
\newcommand\Tstrut{\rule{0pt}{2.6ex}}         % = `top' strut
\newcommand\tstrut{\rule{0pt}{2.0ex}}         % = `top' strut
\newcommand\Bstrut{\rule[-0.9ex]{0pt}{0pt}}   % = `bottom' strut


\usepackage{titling}
\setlength{\droptitle}{-5em}   % This is your set screw

\begin{document}

\end{document}